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Spring Loaded Drinking Straw Hinges

About: When I was young I took all of my toys apart just to see inside. Eventually I learned how to put them back together.
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While browsing Instructables recently I came across a series of 3D printed straw connectors made by amandaghassaei. With theses connectors you can make really intertesting sculptures from plain old drinking straws. I found the sculptures positively amazing, and I got to thinking how cool it would be if there were a to animate them. After studying those connectors, and the original LINX system, I came up with is a small, spring loaded plastic hinge with holes that let thread slip inside of the straw. When a series of the hinges are connected and the string is pulled, the hinges bend and the straws flap about as if they were alive!

Step 1: 3D Printed Parts

I've attached the files for my most recent version of the hinges to this Instructable, feel free to print them as is or modify them to your liking. I've successfully printed these files using an Objet printer and an Up3D printer, and I'm fairly sure they would work well with anything that can extrude ABS. These files were originally designed using 123D beta 9, but I've since moved them over to Inventor Fusion.

If you do choose to design your own, be sure to consider the following:

Flexibility of Material - The inner parts need to flex a bit so that they can snap together

Hinge Pivot Clearance - To provide free movement, the pivot holes in the first half of the hinge need to be a bit larger than the circular pegs on the second half. In this version there is a .01mm gap between the two.

Spring Size - Inside the hinge there are holes exactly the right diameter and depth for the springs I used. If you are starting from scratch, ensure your springs will fit by finding them first and designing around them.

Attachments

Step 2: Hinge Assembly

First of all, you're gunna need some springs. I do not know how to differentiate between springs while ordering them, so I just got a grab bag from Micro-Mark and used some the smaller springs from it; there were about 60 in the bag. The hinges can be used without springs by adding threads to both sides and keeping them taut. This works very well with the hanging version, but not so well with the hand as it's impossible to get the fingers to stand straight without the spring.

I tried several methods of getting the spring inside of the hinges. At first, I snapped the hinge together and then put the spring in with a pair of pliers. That was incredibly difficult and I launched more than a couple springs across the room trying it. After struggling through a dozen hinges I finally came up with this simple way to assemble the them, with the spring, in one simple motion.

Put the spring between the two pieces of hinge before they are snapped together.

With one piece turned 90 degrees, push the two pieces together.

Squeeze the two inner tabs and turn until the parts snap in place.

Step 3: Adding Straws and String

For the straw hand I strung thread though the holes on one side of the hinges and up through the straws. A needle was then heated and poked through the last straw so that the end of the thread could be tied to it (I prefer surgeon knots; they make me think of Alan Alda, and it's the only knot I know.) The long, tentacle like puppet thing from the first video uses thread on both sides of the hinges. Pulling on one thread bends the straws one way, the opposite thread bends them the other.

On the ends of the string I used key ring loops that I could easily slip over my actual fingers. In the pictures you'll notice that the end of the forearm ends in a chopstick and thread, I improvised that bit. It is my firm believe that one can make anything out of chopsticks, thread, and super glue.

In the tentacle, the ends of the two separate threads are connected to another piece of straw and is manipulated like a marionette puppet.

After some testing I found that a lot of drinking straws have a 7.2 mm inside diameter, that is the size these hinges are designed for. Although I do think it would be possible to use smaller straws, it would a challenge to fit a spring down inside of them.

Step 4: Possible Uses

I don't have time to make all the things that I want to make with these hinges. If paired with some angled end-to-end connectors one could build robots, and claws, and a robot hand that hangs over a door and slaps people in the face when they walk in. Or how about motion activated jelly-fish tentacles? Maybe a field of wiggly grass blades? Creepy puppets and Theo Jansen carpet beests? Sure, why not!

Thanks for checking out my wacky straw hinge Instructable. If you are fortunate enough to have access to a 3D printer and need an entertaining distraction, print out a couple of sets of these and have fun! Again, feel free to use and modify the files as you like, but if you make something awesome please share it!

Very good design. The movements are almost lifelike. I think that your design could work well incorporated into a suitable mask as moving tentacles for Cthulhu mythos creatures or insectoid mouth parts.

Great idea and well designed. Perhaps it's easier [and cheaper] to use a strip of semi-flexible plastic as a spring. It only needs to jump back, right? If you choose the right material and thickness, you might even 3D print the spring strip in one go and use it as the hinge at the same time.

Thank you for your kind words, Hmm, it sure would be much easier since it would take the wire springs out of the equation all together and there would only be one piece. Hmmmmm, I'm working with ABS, but that could be made into a curvy shape to help it flex...omg that would work :O Thanks allarrrd, that is brilliant! I'm going to try this later today!

If anybody finds a method for an 'affordable' hinge and spring 'kit', I'd be very interested in getting some - but not at $4 per hinge (and the spring selection not available for shipping to Spain!)...

I uploaded the models to shapeways (here) and it looks like they come out to about $4 for a single hinge. That's a little pricey in my opinion, but I bet you could rig up something similar with a wooden dowel that is slightly wider than the straw.

Instead of a hinge the spring itself could act like a hinge and slots for the thread could be filed into the side of the dowel. Just a thought